Odds significantly favor either over-watering or a high level of soluble salts in the soil - or both, because they usually go hand-in-hand. Misting won't help that particular issue, but the humidity tray offers a very marginal improvement. The primary underlying cause is almost certainly poor root health/function, and it's probably exacerbated by low humidity if you heat in the winter. They also need warm temperatures, so if it's much under 65*, they might start tending to rebel.

It's hard to say exactly what's wrong, and the FIX almost surely lies in that soil choice/watering habits/level of salts in the soil triangle that is pretty inseparable unless you're using an appropriate soil.

If you want to talk soils - let me know & I'll link you to more info here @ GW.

Al

Totally agree. Am also worried this plant is not getting enough light although the entire problem could be the soil/water combo. Hard to know without more info. What way does the window nearest the plant face? How close is it to the window? Are there any heat vents blowing on it or near it?

If it makes you feel any better, this type of plant is one of those that have a much harder time inside a house than most. The environment is just so different from their requirements, and they are usually short-lived, even for many people who have and do well with many other plants.